(1) Field of the Invention
The present invention generally relates to a backlight unit and particularly to a backlight unit with a supporter.
(2) Description of the Prior Art
Liquid Crystal Display (LCD), is previously applied in portable electronic product as notebook PC, cell phone, digital camera, digital video machine or Personal Digital Assistant (PDA). Lately, techniques of making larger sized LCD become matured. This affects the market of display products quite a lot. For example, the desktop-typed LCDs are replacing the traditional CRT monitors. The LCD TV takes advantage of its thinness and lightness to compete with the traditional TV product. Within a LCD, the liquid crystal panel (usually “panel” for short) is an elementary element of the whole device. But the liquid crystal panel does not generate light itself; a back light source is needed for providing light to the panel. Larger sized LCD, about 20″ and larger, usually adopts direct-type backlight unit as its back light source.
Please refer to FIG. 1A. It illustrates a cross section view of a panel and a direct-type backlight unit. As described above, the panel 10 does not generate light itself. So the backlight unit 20 is disposed below the panel 10 to permit a user seeing images presented by panel 10 from top of panel 10.
The backlight unit 20 comprises a bottom cover 22, a plurality of lamp 24 and a diffuser 26. The bottom cover 22 comprises a substrate 221 and sidewalls 223 extending upward from margin areas of the substrate 221. The diffuser 26 is disposed on top of the sidewalls 223 and having a predetermined distance from the substrate 221. The plurality of lamp 24 is disposed between the diffuser 26 and the substrate 221. Each lamp 24 is arranged in a predetermined distance from each other. A light-reflecting material or a reflection sheet 28 is usually applied or disposed on the substrate 221, so as to enhance light-utilizing efficiency of the backlight unit 20.
Each lamp 24 arranged in said predetermined distance to each other is for spread evenly in the backlight unit 20, so as to providing lights of uniform intensity. In another prior art, a single lamp is formed in a curved shape, for example, U-shape (not shown) or W-shape (shown as numeral 24a in FIG. 1B), to achieve the requirement of light uniformity described above.
The diffuser 26 is made from light-transparent material like epoxy. Usually, a predetermined pattern is formed on the diffuser 26 to make light scattering within (diffuser 26). Thus, the backlight unit 20 could provide a more uniform light to the panel 10. This also prevents a user seeing the shape of the lamp 26 and being disturbed when watching the displayed images.
However, some problems are companioned with making larger sized LCDs. When the panel 10 and the backlight unit 20 become larger, a larger diffuser 26 is needed. The diffuser 26 is disposed on top of the sidewalls 223, so only the margin areas of the diffuser 26 are supported. Therefore, the weight of the larger, and also heavier, diffuser 26 would make itself bending at its central part (because of a downward force of gravity). This bending of the diffuser 26 would change its original optical design and defeat the light uniformity. Besides, assemble quality between sidewalls 223 and diffuser 26 may also be defeated because of said weight and bending of diffuser 26. The combination portion of sidewall 223 and diffuser 26 would be loosened or unbound, or even worse, some part of diffuser 26 may be broken.
For the reason described above, a plurality of supporter is adopted between the diffuser 26 and the substrate 221 of the bottom cover 22 to enhance the assemble quality of the backlight unit 20. Typical prior arts about supporter are described below.
Please refer to FIG. 2. FIG. 2 illustrates a cross section view of a typical supporter. Generally, supporter 30 is designed into a cone shape. The cone-shaped supporter 30 has a top end with a smaller cross-section radius L1 and a bottom end with a larger cross-section radius L2. The top end contacts with the diffuser 26, so light could not enter the diffuser 26 in the contact area. The smaller cross-section radius L1 is for minimizing the contact area, so as to prevent an obvious “dark point” occurred in the backlight unit 20. But the supporter 30 is fixed with the substrate 221 by a screw 32, the bottom end with a larger cross-section radius L2 is therefore needed.
However, the prior art described above with FIG. 2 needs an artificial process to assemble the supporter 30 by the screw 32. And there is no automation apparatus for this assemble process hereto, even there is, extra cost would generate. Thus, another prior art is adopted to shorten the artificial process.
Please refer to FIG. 3. FIG. 3 illustrates a cross section view of another prior supporter. Similar to FIG. 2, The supporter 40 has a top end with a smaller cross-section radius L1 and a bottom end with a larger cross-section radius L3. The difference is that the supporter 40 further comprises a column 402, a spring 404 and an anchor 406. The column 402 extends downward from the bottom end of supporter 40. The anchor 406 connects to the bottom of the column 402. The spring 404 surrounds the column 402. As shown in FIG. 3, spring 404 and anchor 406 are separately located at the different sides of the substrate 221 to clip it between. A ring 42 could also be adopted at the side of anchor 406 to enhance the clipping performance. Within, the anchor 406 is shrinkable when passing through the hole of the substrate 221, once and irreversible. While assembling, disposing the ring 42 on the bottom surface of the substrate 221, then only a simple plugging action is needed.
Although the prior supporter 40 shown in FIG. 3 is much easier to be assembled, however, the spring 404 limits its supporting ability. When an external force, which is larger than the elastic force of the spring 404, applies to the diffuser 26, the supporter 40 would slide within a distance (symbol “d” in FIG. 3). Besides, once the spring 40 becomes tired, the supporting ability may entirely lose.
Beside the remaining disadvantages of the described prior arts of FIG. 2 and FIG. 3, they have another common drawback. That is, although the supporter 30 or 40 is designed into a cone shape to minimize the contact area with the diffuser 26. The bottom end of supporter 30 or 40 still prevents the contact portion of reflection sheet 28 reflecting light upward. Comparing to other portion of reflection sheet 28, which is not contact with supporter 30 or 40, the contact portion would have relatively weaker brightness and become a “shadow point” of the backlight unit 20.